High frequency communication systems use a high frequency band of, for example, 2 GHz or greater to perform high speed and large-volume communications. As a filter for high frequency devices, there has been known laterally coupled multi-mode monolithic filters using a piezoelectric film having a high acoustic velocity. The laterally coupled multi-mode monolithic filter has a structure designed to have a ground electrode and a signal electrode formed across a piezoelectric film. The signal electrode includes two or more electrodes to which signals are applied as disclosed in, for example, Japanese Patent Application Publication Nos. 2009-188484 and 2009-188599.
However, the aspect ratio of the signal electrode may increase when the input and output impedance of the filter is adjusted. The increase in the aspect ratio of the signal electrode causes the concentration of stress on the piezoelectric film and may cause cracks or the like. Alternatively, acoustic waves may leak in the lateral direction of the signal electrode.